Globe warm in 2012, but not as hot as USA

Jan. 16, 2013
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The sun sets behind the Christ the Redeemer statue and the Corcovado mountain Dec. 28 in Rio de Janeiro, two days after the city recorded its hottest day since 1915 at 109.7 degrees Fahrenheit. / Felipe Dana, AP

by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

While the USA sweltered through its warmest year on record in 2012, the globe as a whole wasn't quite that toasty.

Last year was the 10th-warmest year on record globally, according to data released Tuesday by the National Oceanic and Atmospheric Administration (NOAA). Another temperature analysis from NASA showed the year was the ninth-warmest on record.

According to NOAA data, 2012 marked the 36th consecutive year that the yearly global temperature was above average. All 12 years in the 21st century (2001â??2012) rank among the 14 warmest in the 133-year period of record keeping.

NOAA and NASA independently produce a record of the Earth's surface temperatures and changes based on historical observations over the land surface and oceans. The agencies' final results can vary slightly, as they use different methods to analyze the data.

Both agencies reported the global temperature was about 1 degree Fahrenheit above average in 2012. Global climate records go back to 1880.

Why should we care about a temperature reading that's only 1 degree above average?

"A 1-degree rise in surface temperature may sound small when considering only the temperature," said Deke Arndt, chief of the climate monitoring branch of NOAA's National Climatic Data Center. "But that 1-degree change can alter global circulation patterns, which control areas of heat and drought.

"A warmer atmosphere can 'hold' more water vapor, which makes it more energetic and more prone to carry and deliver large precipitation in single doses," Arndt said. "A persistently warmer Arctic and near-Arctic puts more melting stress on ice sheets and sea ice ... which accelerates the warming. An upper ocean that warms by a degree or so will expand, contributing significantly to sea-level rise."

The North American warmth, which pushed the USA to its warmest year on record, was "remarkable," said Tom Karl, director of the National Climatic Data Center in Asheville, N.C., during a news conference Tuesday. "We've broken the record by more than 1 degree, that is quite impressive. It literally smashed the record."

The global annual temperature has increased at an average rate of 0.11 degree per decade from 1880 to 2012, NOAA reported.

The long-term warming trend, including the continual warming since the mid-1970s, "has been conclusively associated" with the production of human-made greenhouse gases, which began to grow substantially early in the 20th century, said NASA climate scientist James Hansen.

He said the global temperature has been essentially "flat" for the past several years and attributes that to a combination of factors, which could include solar variability, increasing atmospheric aerosols that help cool the atmosphere, the global economic downturn, and a dominant La NiÃ±a over the past few years.

La NiÃ±a is a cooling of tropical Pacific Ocean water that tends to cool temperatures around the world, and 2012 marked the warmest La NiÃ±a year since at least 1950, NOAA reported.

"One more year of numbers isn't in itself significant," NASA climatologist Gavin Schmidt said in a news release. "What matters is this decade is warmer than the last decade, and that decade was warmer than the decade before. The planet is warming."